The present invention relates to optical imaging systems that sweep an output beam across an image plane surface as successive raster scan lines and, more particularly, to means for adjusting the optical center line of the scanning beams.
Optical imaging systems, such as printers, copiers, and facsimile machines which utilize a laser beam as a light source have come into wide use. A typical raster output system (ROS) output from a laser is collimated, focused by suitable optics, deflected from the facets of a rotating polygon scanner and scanned across a photoreceptor surface as modulated scan lines. Diode lasers have come to be preferred over gas lasers. A consistent problem has been the difficulty of aligning the collimated modulated diode laser outputs with the optical elements that are commonly mounted within a ROS housing. The alignment of the optical center line of the diode laser and the collimating lens with the center line of the collimating lens housing (barrel) has proved especially difficult. There are various prior art techniques for achieving this alignment; a useful summary of the references is contained in U.S. Pat. No. 5,111,476, whose contents are hereby incorporated by reference. Many of the techniques disclosed in this patent require an adhesive or glue to be applied to the optical elements to maintain a final alignment. The present invention is directed towards a mechanical alignment method which utilizes two pairs of eccentric rings located in grooves at each end of the collimator lens barrel. A rough initial alignment of diode to lens is implemented which leaves the optical and mechanical center lines of the barrel still out of specified alignment. The eccentric rings are rotated while viewing a scan line on a camera sensor located at an image plane until a final specific alignment is achieved. More particularly the present invention relates to a method for adjusting the optical center line of scanning beams generated in a Raster Output Scanner (ROS) system including the steps of:
generating a modulated laser output beam, PA1 collimating the modulated laser output beam by means of collimating lens elements mounted with a lens barrel to produce a collimated output beam, PA1 scanning the collimated output beam across the surface of an image plane as a series of raster scan lines and PA1 moving said lens barrel to change the optical center line of the collimated output beam until the scan lines are centered along a desired optical center line.